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More than half of the familial cutaneous melanomas have unknown genetic predisposition. This study aims at characterizing a novel melanoma susceptibility gene.

Supplemental Digital Content is available in the text.Introduction of targeted therapy in the treatment of metastatic cutaneous malignant melanoma (CMM) has improved clinical outcome during the last years. However, only in a subset of the CMM patients, this will lead to long-term effects. CEBPB is a transcription factor that has been implicated in various physiological and pathological processes, including cancer development. We have investigated its prognostic impact on CMM and unexpectedly found that higher CEBPBmRNA levels correlated with a longer overall survival. Furthermore, in a small cohort of patients with metastatic CMM treated with BRAF-inhibitors, higher levels of CEBPBmRNA expression in the tumor cells prior treatment correlated to a longer progression-free survival. We have characterized an overlapping antisense transcript, CEBPB-AS1, with the aim to investigate the regulation of CEBPB expression in CMM and its impact on BRAF-inhibitor sensitivity. We demonstrated that silencing of CEBPB-AS1resulted in epigenetic modifications in the CEBPB promoter and in increased CEBPBmRNA and protein levels, inhibited proliferation and partially resensitized BRAF-inhibitor resistant CMM cells to this drug-induced apoptosis. Our data suggest that targeting CEBPB-AS1may represent a valuable tool to sensitize CMM cells to the BRAF-inhibitor-based therapies.

Cutaneous malignant melanoma (CMM) is the deadliest form of skin cancer and clinically challenging due to its propensity to develop therapy resistance. Reactive oxygen species (ROS) can induce DNA damage and play a significant role in CMM. MTH1 protein protects from ROS damage and is often overexpressed in different cancer types including CMM. Herein, we report that MTH1 inhibitor TH1579 induced ROS levels, increased DNA damage responses, caused mitotic arrest and suppressed CMM proliferation leading to cell death both in vitro and in an in vivo xenograft CMM zebrafish disease model. TH1579 was more potent in abrogating cell proliferation and inducing cell death in a heterogeneous co-culture setting when compared with CMM standard treatments, vemurafenib or trametinib, showing its broad anticancer activity. Silencing MTH1 alone exhibited similar cytotoxic effects with concomitant induction of mitotic arrest and ROS induction culminating in cell death in most CMM cell lines tested, further emphasizing the importance of MTH1 in CMM cells. Furthermore, overexpression of receptor tyrosine kinase AXL, previously demonstrated to contribute to BRAF inhibitor resistance, sensitized BRAFmutant and BRAF/NRASwildtype CMM cells to TH1579. AXL overexpression culminated in increased ROS levels in CMM cells. Moreover, silencing of a protein that has shown opposing effects on cell proliferation, CAV-1, decreased sensitivity to TH1579 in a BRAF inhibitor resistant cell line. AXL-MTH1 and CAV-1-MTH1 mRNA expressions were correlated as seen in CMM clinical samples. Finally, TH1579 in combination with BRAF inhibitor exhibited a more potent cell killing effect in BRAFmutant cells both in vitro and in vivo. In summary, we show that TH1579-mediated efficacy is independent of BRAF/NRASmutational status but dependent on the expression of AXL and CAV-1.

Most genetic susceptibility to cutaneous melanoma remains to be discovered. Meta-analysis genome-wide association study (GWAS) of 36,760 cases of melanoma (67% newly genotyped) and 375,188 controls identified 54 significant (P< 5 × 10−8) loci with 68 independent single nucleotide polymorphisms. Analysis of risk estimates across geographical regions and host factors suggests the acral melanoma subtype is uniquely unrelated to pigmentation. Combining this meta-analysis with GWAS of nevus count and hair color, and transcriptome association approaches, uncovered 31 potential secondary loci for a total of 85 cutaneous melanoma susceptibility loci. These findings provide insights into cutaneous melanoma genetic architecture, reinforcing the importance of nevogenesis, pigmentation and telomere maintenance, together with identifying potential new pathways for cutaneous melanoma pathogenesis.

Supplemental Digital Content is available in the text.Germline mutations of BRCA1and BRCA2predispose individuals to a high risk of breast and ovarian cancer, and elevated risk of other cancers, including those of the pancreas and prostate. BRCA2mutation carriers may have increased risk of uveal melanoma (UM) and cutaneous melanoma (CM), but associations with these cancers in BRCA1mutation carriers have been mixed. Here, we further assessed whether UM and CM are associated with BRCA1or BRCA2by assessing the presence, segregation and reported/predicted pathogenicity of rare germline mutations (variant allele frequency < 0.01) in families with multiple members affected by these cancers. Whole-genome or exome sequencing was performed on 160 CM and/or UM families from Australia, the Netherlands, Denmark and Sweden. Between one and five cases were sequenced from each family, totalling 307 individuals. Sanger sequencing was performed to validate BRCA1and BRCA2germline variants and to assess carrier status in other available family members. A nonsense and a frameshift mutation were identified in BRCA1, both resulting in premature truncation of the protein (the first at p.Q516 and the second at codon 91, after the introduction of seven amino acids due to a frameshift deletion). These variants co-segregated with CM in individuals who consented for testing and were present in individuals with pancreatic, prostate and breast cancer in the respective families. In addition, 33 rare missense mutations (variant allele frequency ranging from 0.00782 to 0.000001 in the aggregated ExAC data) were identified in 34 families. Examining the previously reported evidence of functional consequence of these variants revealed all had been classified as either benign or of unknown consequence. Seeking further evidence of an association between BRCA1variants and melanoma, we examined two whole-genome/exome sequenced collections of sporadic CM patients (total N= 763). We identified one individual with a deleterious BRCA1variant, however, this allele was lost (with the wild-type allele remaining) in the corresponding CM, indicating that defective BRCA1was not a driver of tumorigenesis in this instance. Although this is the first time that deleterious BRCA1mutations have been described in high-density CM families, we conclude that there is an insufficient burden of evidence to state that the increased familial CM or UM susceptibility is because of these variants. In addition, in conjunction with other studies, we conclude that the previously described association between BRCA2mutations and UM susceptibility represents a rare source of increased risk.

Germline mutations in CDKN2Aare frequently identified among melanoma kindreds and are associated with increased atypical nevus counts. However, a clear relationship between pathogenic CDKN2Amutation carriage and other nevus phenotypes including counts of common acquired nevi has not yet been established. Using data from GenoMEL, we investigated the relationships between CDKN2Amutation carriage and 2-mm, 5-mm, and atypical nevus counts among blood-related members of melanoma families. Compared with individuals without a pathogenic mutation, those who carried one had an overall higher prevalence of atypical (odds ratio = 1.64; 95% confidence interval = 1.18–2.28) nevi but not 2-mm nevi (odds ratio = 1.06; 95% confidence interval = 0.92–1.21) or 5-mm nevi (odds ratio = 1.26; 95% confidence interval = 0.94–1.70). Stratification by case status showed more pronounced positive associations among non-case family members, who were nearly three times (odds ratio = 2.91; 95% confidence interval = 1.75–4.82) as likely to exhibit nevus counts at or above the median in all three nevus categories simultaneously when harboring a pathogenic mutation (vs. not harboring one). Our results support the hypothesis that unidentified nevogenic genes are co-inherited with CDKN2Aand may influence carcinogenesis.

The genetic background of cutaneous malignant melanoma (CMM) includes both germ line aberrations in high-penetrance genes, like CDKN2A, and allelic variation in low-penetrance genes like the melanocortin-1 receptor gene, MC1R. Red-hair colour associated MC1Ralleles (RHC) have been associated with red hair, fair skin and risk of CMM. We investigated MC1Rand CDKN2Avariation in relation to phenotype, clinical factors and CMM risk in the Swedish population. The study cohort consisted of sporadic primary melanoma patients, familial melanoma patients and a control group. An allele-dose dependent increase in melanoma risk for carriers of variant MC1Ralleles (after adjusting for phenotype), with an elevated risk among familial CMM patients, was observed. This elevated risk was found to be significantly associated with an increased frequency of dysplastic nevi (DN) among familial patients compared to sporadic patients. MC1Rvariation was found to be less frequent among acral lentiginous melanomas (ALM) and dependent on tumour localisation. No association was found between CDKN2Agene variants and general melanoma risk. Two new variants in the POMCgene were identified in red haired individuals without RHC alleles.